Wave mapping: detection of co-existing multiple wavefronts in high-resolution electrical mapping

Modeling and experimental approaches for elucidating multi-scale uterine smooth muscle electro- and mechano-physiology: A review

The uterus provides protection and nourishment (via its blood supply) to a developing fetus, and contracts to deliver the baby at an appropriate time, thereby having a critical contribution to the life of every human. However, despite this vital role, it is an under-investigated organ, and gaps remain in our understanding of how contractions are initiated or coordinated. The uterus is a smooth muscle organ that undergoes variations in its contractile function in response to hormonal fluctuations, the extreme instance of this being during pregnancy and labor. Researchers typically use various approaches to studying this organ, such as experiments on uterine muscle cells, tissue samples, or the intact organ, or the employment of mathematical models to simulate the electrical, mechanical and ionic activity. The complexity exhibited in the coordinated contractions of the uterus remains a challenge to understand, requiring coordinated solutions from different research fields. This review investigates differences in the underlying physiology between human and common animal models utilized in experiments, and the experimental interventions and computational models used to assess uterine function. We look to a future of hybrid experimental interventions and modeling techniques that could be employed to improve the understanding of the mechanisms enabling the healthy function of the uterus.

Comparison of gold and PEDOT:PSS contacts for high-resolution gastric electrical mapping using flexible printed circuit arrays

Motility of the stomach is governed by an electrophysiological event termed gastric slow waves. High-resolution (HR) bioelectrical mapping involves placing array of electrodes over the surface of the stomach to record gastric slow waves. Conductive polymer materials have recently been applied to great effect in cardiology and neurophysiology due to its compliant and biocompatible properties. The aim of this study was to quantify the performance of poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) deposited on a flexible print circuit electrode array for gastric slow wave HR mapping. The Au electrodes were coated with PEDOT:PSS at 1 V and different levels of charges (0.3-1.2 mC). HR mapping alongside standard Au electrodes was performed in three anesthetized pigs. Overall, the PEDOT:PSS electrodes detected both antegrade and retrograde slow wave propagations, with comparable frequency, velocity and signal-to-noise ratio to the Au electrodes. Differences between the two electrodes were noted in terms of amplitude and downstroke gradient. The findings of this study will inform designs of future stretchable and implantable HR mapping electrode arrays for gastrointestinal recording and stimulation therapies.

A pipeline for phase-based analysis of in vitro micro-electrode array recordings of gastrointestinal slow waves

Motility of the gastrointestinal tract (GI) is governed by an bioelectrical event termed slow waves. Accurately measuring the characteristics of GI slow waves is critical to understanding its role in clinical applications. High-resolution (HR) bioelectrical mapping involves placing a spatially dense array of electrodes directly over the surface of the GI wall to record the spatiotemporal changes in slow waves. A micro-electrode array (MEA) with spatial resolution of 200 μm in an 8x8 configuration was employed to record intestinal slow waves using isolated tissues from small animals including rodents, shrews and ferrets. A filtering, processing, and analytic pipeline was developed to extract useful metrics from the recordings. The pipeline relied on CWT and Hilbert Transform to identify the frequency and phase of the signals, from which the individual activation times of slow waves were identified and clustered using k-means. A structural similarity index was applied to group the major activation patterns. Overall, the pipeline identified 91 cycles of slow waves from 300 s of recordings in mice, with an average frequency of 20.68 ± 0.71 cpm, amplitude of 7.94 ± 2.15 µV, and velocity of 3.64 ± 1.75 mm s^-1. Three major propagation patterns were identified during this period. The findings of this study will inform the development of a high throughput software platform for future in vitro pharmacological studies using the MEA.

A Framework for Spatiotemporal Analysis of Gastrointestinal Spike Burst Propagation

Gastrointestinal spike bursts are a bioelectrical phenomenon associated with motility. These events when initiated propagate a small distance and abruptly terminate activating a small area defined as a patch. Understanding normal and abnormal propagation patterns of these events may shed light on the root causes of functional motility disorders. This study develops an automated framework for spatiotemporal analysis of spike bursts. High-resolution electrical signals were obtained from the pig intestine, after which intestinal spike bursts were identified and clustered into their propagating wavefronts. Propagation velocity was estimated by fitting a polynomial surface to the activation times. The fit was able to estimate the velocity of spike burst patches covering at least six channels with an average RMSE of 0.4 s. Propagation within patches was visualized by plotting the fit as activation maps and velocity maps. Average velocities were calculated to compare the propagation characteristics of different types of patches. In the future, this framework will be extended to generate amplitude maps and spike burst duration maps. These tools can be used to analyze spike patch propagation and their relationship to motility.

A system and method for online high-resolution mapping of gastric slow-wave activity

High-resolution (HR) mapping employs multielectrode arrays to achieve spatially detailed analyses of propagating bioelectrical events. A major current limitation is that spatial analyses must currently be performed "off-line" (after experiments), compromising timely recording feedback and restricting experimental interventions. These problems motivated development of a system and method for "online" HR mapping. HR gastric recordings were acquired and streamed to a novel software client. Algorithms were devised to filter data, identify slow-wave events, eliminate corrupt channels, and cluster activation events. A graphical user interface animated data and plotted electrograms and maps. Results were compared against off-line methods. The online system analyzed 256-channel serosal recordings with no unexpected system terminations with a mean delay 18 s. Activation time marking sensitivity was 0.92; positive predictive value was 0.93. Abnormal slow-wave patterns including conduction blocks, ectopic pacemaking, and colliding wave fronts were reliably identified. Compared to traditional analysis methods, online mapping had comparable results with equivalent coverage of 90% of electrodes, average RMS errors of less than 1 s, and CC of activation maps of 0.99. Accurate slow-wave mapping was achieved in near real-time, enabling monitoring of recording quality and experimental interventions targeted to dysrhythmic onset. This work also advances the translation of HR mapping toward real-time clinical application.

Automated gastric slow wave cycle partitioning and visualization for high-resolution activation time maps

High-resolution (HR) multi-electrode mapping has become an important technique for evaluating gastrointestinal (GI) slow wave (SW) behaviors. However, the application and uptake of HR mapping has been constrained by the complex and laborious task of analyzing the large volumes of retrieved data. Recently, a rapid and reliable method for automatically identifying activation times (ATs) of SWs was presented, offering substantial efficiency gains. To extend the automated data-processing pipeline, novel automated methods are needed for partitioning identified ATs into their propagation cycles, and for visualizing the HR spatiotemporal maps. A novel cycle partitioning algorithm (termed REGROUPS) is presented. REGROUPS employs an iterative REgion GROwing procedure and incorporates a Polynomial-surface-estimate Stabilization step, after initiation by an automated seed selection process. Automated activation map visualization was achieved via an isochronal contour mapping algorithm, augmented by a heuristic 2-step scheme. All automated methods were collectively validated in a series of experimental test cases of normal and abnormal SW propagation, including instances of patchy data quality. The automated pipeline performance was highly comparable to manual analysis, and outperformed a previously proposed partitioning approach. These methods will substantially improve the efficiency of GI HR mapping research.

Electrical inhibition of preterm birth: inhibition of uterine contractility in the rabbit and pup births in the rat

OBJECTIVE

The purpose of this study was to inhibit uterine contractility during parturition with an electrical current, which is called electrical inhibition, in the rabbit and the rat.

STUDY DESIGN

We studied the electrical inhibition of in vitro spontaneously contracting preterm or term gestational rat myometrium tissue and in vivo spontaneously contracting uterus either directly in the rabbit and rat or transvaginally in the rat. Values for myometrial tension, intrauterine pressure, pup birth intervals, and electromyographic activity before and after electrical inhibition were compared.

RESULTS

Electrical inhibition decreased rat in vitro myometrial tension by 50%, decreased in vivo rabbit intrauterine pressure by 48%, decreased in vivo rat intrauterine pressure by 80%, and increased birth intervals (latency) by factors of 50 (direct electrical inhibition) and 20 (transvaginal electrical inhibition). All electromyographic activity parameters were reduced significantly.

CONCLUSION

Electrical inhibition of the uterus is possible. Electrical inhibition is rapid and localized; the duration can be prolonged, and the reversibility is spontaneous. Electrical inhibition may be a new method of tocolysis in the human.

The spatial behaviour of spike patches in the feline gastroduodenal junction in vitro

In the isolated feline gastroduodenal region, the spatial propagation of slow waves and of individual spikes was reconstructed. Recordings were performed simultaneously from 240 extracellular electrodes positioned on the serosal surface across the junction. Results from nine experiments (22 slow waves) showed that the slow wave never propagated across the gastroduodenal region and that this block was due to the presence of a zone of quiescence caudal to the pylorus. In contrast, spikes (n=155) were able to propagate into the quiescent zone, either from the antrum (15.4%) or from the duodenum (34.0%) and occasionally, were able to propagate from one organ to the other (10.9%). However, in all cases, spike conduction was self-limited and activated a local area termed a 'patch'. The length of the patches located in the gastroduodenal region was significantly longer than in the rest of the duodenum (20.2 mm +/- 9. 7 vs. 9.5 mm +/- 3.2; P < 0.001) indicating a possible enhancement of spike propagation in this region. In conclusion, in spite of the total conduction block for slow waves, individual spikes are able to propagate across the gastroduodenal region, albeit in self-limited areas or 'patches'. These spike patches could form the building blocks for gastroduodenal coordination.

Propagation of individual spikes as "patches" of activation in isolated feline duodenum

Asynchrony of spikes has made it difficult to study the spatial and temporal behavior of spikes in the gastrointestinal system. By simultaneously recording from a large number of closely spaced electrodes, we investigated the propagation of individual spikes. Recordings were performed from the serosal surface of the isolated feline duodenum at 240 sites simultaneously. Analysis of the tracings made it possible to reconstruct the propagation of individual spikes. Spikes propagate in the longitudinal and circumferential directions in self-limiting areas or "patches." Conduction within patches may occur in the orad or aborad direction irrespective of the direction of the slow wave. Most of the patches are smaller (<40 mm(2)), although inhomogeneous activation by the preceding slow wave may increase their size. Stimulation by ACh, TTX, or tetraethylammonium does not affect the average patch size but does increase significantly their number and distribution in the duodenum [from 26% (control) to 56%, 61%, and 72%, respectively]. In conclusion, individual spikes activate limited areas or patches in the small intestine, and pharmacological stimulation increases the number and distribution of these patches. In the small intestine, this pattern of activation would induce localized contractions. Contraction could be modulated by the size, number, and distribution of spike patches.

High resolution electrical mapping in the gastrointestinal system: initial results

High resolution electrical mapping in the gastrointestinal system entails recording from a large number of extracellular electrodes simultaneously. It allows the collection of signals from 240 individual sites which are then amplified, filtered, digitized, multiplexed and stored on tape. After recording, periods of interest can be analysed and the original sequence of activity reconstructed. This technology, originally developed to study normal rhythms and abnormal dysrhythmias in the heart, has been modified to allow recordings from the gastrointestinal tract. In this report, initial results are presented describing the origin and propagation of the slow wave in the isolated stomach and the isolated duodenum in the cat. These results show that in both organs it not uncommon to have more than one focus active during a single cycle. The conduction of slow waves from such a multiple pacemaker environment can become quite complex, and this may play a role in determining the contractile pattern in these organs.